<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>el:挂载点</title>
</head>
<body id ="body">
  <h2 id="app" class="app">
      {{message}}
      <span>{{message}}</span>
      </h2>
  <!-- 开发环境版本，包含了有帮助的命令行警告--> 
  <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
  <script>
      var app=new Vue({
          // el:"#app",
          // el:".app",
          // el:"div",
          el:"#body",
          data:{
              message:"黑马程序员！"
          }
      })
  </script>
</body>
</html>